An apparent relationship between geomagnetic disturbances and changes in atmospheric circulation at 300 millibars

This paper describes a study of the average contour length changes and trough developments at the 300-mb level following geomagnetic disturbances from October 1956 through March 1957. A ‘contour length index’ and a ‘trough index’ were developed to measure the degree of disturbance of the 300-mb circulation over western North America and the eastern Pacific Ocean and the intensity of troughs in this circulation. Three trough classifications were defined and the development of all troughs appearing in the Aleutian Island-Gulf of Alaska area were analyzed by class. The results suggest that troughs which appeared in the Aleutian Island-Gulf of Alaska area a few days after an abrupt increase in geomagnetic activity subsequently developed a stronger average cyclonic curvature than other troughs. The largest trough developments and the maximum contour lengths occurred, on the average, eight to nine days after the magnetic disturbance. Added studies will be needed to determine whether the suggested relationships are general ones.